Flux for use in the treatment of light metal



Patented Nov. 11, 1941 FLUX FOR USE IN THE TREATMENT OF mom METAL Harry Rowland Leech, Salford, and Gordon James Lewis, Eccles, near Manchester, England, assignors to Magnesium Elektron Limited, London, England, a British company No Drawing. Application December 5, 1940, Se-

rial No. 368,733. In Great Britain November 2 Claims.

This invention relates to fluxes used for refining and/or protecting against oxidation light metals consisting of magnesium, magnesium base alloys and aluminium base alloys containing magnesium, all referred to hereinafter as metal.

For preventing contact of the metal with the air during melting so as to avoid oxidation of the metal, it has been proposed to use a flux of low melting point which is thinly fluid when molten. The use of such a flux, however, is not so suitable after the initial melting up stage since the molten film. of flux is easily broken by agitation and there is a tendency for traces of such fiux to remain in the metal when cast with consequent harmiul effects. It is, therefore, our practice to use an inspissated fiux after initial melting up. The principle of this flux was first disclosed in the specification of the applicant companys Patent No. 219,287.

The object of the present invention is to provide an improved inspissated type of flux.

.An inspissated flux should, when spread on the surface of the molten metal, give a pasty, viscous cover or crust. Such a crust should cover the whole exposed surface of the metal and should not, by movement of the metal, be broken up or detached into separate p eces which would permit access of air to the metal surface. The crust should move with the movement of the metal surface, e. g. if the crucible in which the metal is contained is tilted to pour out the metal, the crust should still cover the surface.

The flux should also be capable of refining the metal. If a non-inspissated flux has been used during the melting process, it, together with oxides, etc. which may have been formed at the same time, or which were present previously, will tend when melting is completed to be disseminated throughout the molten metal and must be removed if the castings produced from the molten metal are to have optimal properties for example as regards mechanical strength and corrosion resistance. The lnspissated flux, when stirred in the molten metal, can have an inspissating or agglomerating action on the impurities therein, which facilitates the rapid settling out of these impurities. Moreover, the flux should be capable of maintaining good contact with the sides of the crucible and should not have an unduly restrictive effect upon the escape of gases from the metal.

The final criteria of the best flux are:

1. The casting made by its use shall have the best possible mechanical properties and corrosion resistance, and minimum content of impurities especially chlorides.

2. The losses due to oxidation whilst molten shall be minimal.

3. Although of not such importance, it is nevertheless desirable that the flux should be economical in ,use, i. e. excessive quantities should not be required to give the desired results.

We have carried out a considerable amount of experiment with many different kinds of ingredicuts and widely varying percentages with a view to producing a fiux which will give a consistently good result. In testing these various fluxes We have finally after satisfying the above-mentioned criteria, relied upon foundry experience on matters such as consistency of the flux in use and maintaining good contactwith the sides of the crucible.

As a result of our experiments, we have found that good results are obtained with mixtures within the following range:

Per cent Magnesium chloride 30-50 Calcium chloride 8-16 Sodium chloride -1 1 Up to 15 Potassium chloride Up to 15 Magnesium oxide 5--20 Calcium fluoride 2 15-25 Together between 5 and 25 7 Together within the limits 2%45% Per cent Magnesium chloride 3'7 Calcium chloride 14 Sodium chloride, potassium chloride l5 Magnesium oxide 13 Calcium fluoride 21 These constituent materials should be ground to give a. powder which preferably passes through a 10 mesh B. S. sieve but not more than 20% ofwhich passes through a 200 B. S. sieve. If desired, the ingredients other than the magnesium oxide and calcium fluoride may be fused together and subsequently ground and mixed with the magnesium oxide and calcium fluoride.

- Per cent Magnesium chloride 34 Calcium chloride 30 Sodium and potassium chlorides 35 Magnesium oxide 1 As melting proceeded more flux of the same composition was added to control burning of the metal; in all kgs. of the fluid flux was used. When melting was complete, heating was continued until the contents of the pot had been I brought to a temperature of 745 C., whereupon the metal was agitated by plunging with an iron tool. The molten metal was then treated with 7.25 kgs. of a flux of the following composition:

Per cent Magesium chloride 37 Calcium chloride 14 Sodium and potassium chlorides 15 Magnesium oxide 13 Calcium fluoride 21 This quantity of flux was applied in the following manner. A portion of the flux was stirred into the metal by plunging as above and then the remainder was sprinkled uniformly over the surface to form a protective cover and "the metal allowed to stand and cool to 720 C.,

whereupon it was poured into ingots. The yield thus obtained was 2,196 kgs. (96.1% melting efficiency) of metal containing 0.005% chloride ion.

From the metal thus prepared, alloys according to normal D. T. D. specifications were manufactured and test specimens from these alloys showed a corrosion resistance and mechanical properties which were at least as good as such alloys as heretofore produced. In producing such alloys, the purified magnesium was remelted and alloyed with the aid of the fluid flux, the melt was then further protected by means of the inspissated flux and the usual superheating and settling processes, where necessary, were carried out in accordance with applicant companys Patents Nos. 359,425 and 336,498.

We claim:

1. A flux for use with metal of the kind hereinbefore defined having the following composition:

Per cent Magnesium chloride -50 Calcium chloride 8-16 Sodium chloride Up to 15 Potassium chloride Up to 15 Magnesium oxide 5-20 Calcium fluoride 15-25 the sodium chloride and potassium chloride together amounting to between 5% and 25% and the magnesium oxide and calcium fluoride t0- gether amounting to between 25% and and the total of all these ingredients amounting to at least 2. A flux for use with metal of the kind hereinbefore defined having the following composition:

Per cent Magnesium chloride 35-40 Calcium chloride 12-16 Sodium chloride 1 1347 Potassium chloridel Magnesium oxide 11-15 Calcium fluoride 19-23 the total of all these ingredients amounting to at least 95%.

HARRY ROWLAND LEECH. GORDON JAMES LEWIS. 

